1. Field of the Invention
The present invention relates to a machine tool machining an inner surface to be machined located on an inner surface of a workpiece, and to a workpiece inner surface machining method using the machine tool.
2. Description of the Related Art
As a conventional machine tool machining a spherical surface to be machined such as, for example, an inner surface of a differential gear case of an automobile, there is one described in U.S. Pat. No. 6,318,220B1, for instance. This machine tool uses a tool having a supporting member and a bar-shaped cutting tool supported by the supporting member to be pivotable about a pivot axis orthogonal to an axis of the supporting member. The cutting tool has cutting edges at its one end and another end and is pivotably supported so as to eject/retract from/into the supporting member. At the time of the machining, the tool is inserted into a workpiece while the cutting tool is held at a retracted position, and the cutting tool is pivoted about the pivot axis, so that the cutting edges cut the inner surface of the workpiece into an arcuate shape. Subsequently, the supporting member is slightly rotated about its axis and the cutting tool is pivoted again about the pivot axis. By repeating this operation, the inner surface of the workpiece is machined into a spherical shape.
The machining method described in the aforesaid U.S. Pat. No. 6,318,220B1 is capable of machining the inner surface of the workpiece into the spherical shape, but is not capable of machining a bearing surface which is a flat surface orthogonal to the axis of the supporting member. Another tool is used to machine the bearing surface.